In a sign of hope for Japan, new US Trade Representative Robert Lighthizer will attend a meeting of trade ministers from the 21 Asia-Pacific Economic Cooperation (Apec) countries on Thursday (May 18) and Friday (May 19) in the Vietnamese capital of Hanoi.

New Zealand Trade Minister Todd McClay told Radio New Zealand the USA and other non-TPP countries will benefit from the changes to the sharing of pharmaceutical information.

"I think we got better than I'd expected".

TPP rules have to be changed so it can take effect without US participation, but Japanese Finance Minister Taro Aso last month said Tokyo would not rule out the option of negotiating such a deal.

According to a joint press release, Abe and English "remain committed to maintaining the unity among the signatories and early entry into force of the TPP agreement".

English said Abe clearly saw Japan playing a leadership role and it was standing together with New Zealand in trying to generate "momentum" and have others back implementation.

"Unbelievably they plan to retain the existing text, with all the toxic rules the U.S. insisted on that undermine affordable medicines, grant foreign investors special rights to enforce offshore, prohibit requirements for data to be held onshore, and more", she said.

"The TPP remains valuable both economically and strategically for New Zealand".